The $28K Sandwich That Grew No Mold

How the Virgin Mary's grilled cheese stayed mold-free for 10 years.

With a winning bid of $28,000, the online casino GoldenPalace.com won the auction for one of eBay's most coveted oddities: a 10-year-old grilled cheese sandwich, one side of which bears the Virgin Mary's image. The seller, Diana Duyser of Hollywood, Fla., claims that the sandwich never sprouted a single spore of mold, despite having been stored in a less-than-airtight plastic box. Is it possible for a decade-old sandwich to remain mold-free without divine intervention?

The odds are against a pristine sandwich, but it's hardly impossible. The fact that Duyser's sandwich was a grilled cheese was likely its saving grace, assuming she followed the traditional American recipe. The homespun favorite is usually prepared either by slathering the bread with margarine or by cooking it in a pan or press that's been well-lubed with the fatty butter substitute. Margarine consists primarily of hydrogenated vegetable oil, which is rich in trans fats. The fungi that love bread are typically averse to trans fats—they don't digest them well.

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The cheese filling, aside from contributing to the sandwich's fat content, also added calcium to the mix. Calcium is a mild mold retardant, though less so than margarine. The acidic cheese may have also altered the pH level of the sandwich; bread mold grows best when the pH is more or less neutral.

It's not clear what sort of bread Duyser used, but odds are it was a store-bought loaf. Such breads are almost always chock full of preservatives like sorbic acid and propionic acid, which help to ward off mold. It's possible that these preservatives helped keep the sandwich mold-free—Wonder Bread, for example, can fend off mold for an extended period, provided it's not kept in too moist an environment.

The fact that the sandwich was cooked may also have played a big role in keeping the fungi away. Think back to one of the most common grade-school science experiments, growing mold on white bread. One of the key steps is adding a few drops of water to the slice before placing it in a plastic bag or container. This is because bread mold thrives in damp conditions. A crispy grilled cheese, by contrast, has had most of its water removed and so is not as inviting a meal for passing mold spores.

Still, the sandwich's lack of mold is perhaps even more remarkable than the visage of the Virgin Mary that some see in its nooks and crannies. It's certainly much more impressive than another eBay item now on sale, a grilled cheese featuring the likeness of Hello Kitty. As of this writing, the top bid is $0.80.